Light micrograph of the marine diatom Achnanthes spec. Achnanthes forms short chains, the cells remain loosely attached. Achnanthes lives epiphytically on aquatic plants and any other substrates, in this picture attached to an Oscillatoria filament. The specimens are from the North Sea, German Bight. The relatively cool northern seas harbor very large quantities of these primary producers, which autotrophically form the base of the food chain. At the same time the diatoms of the oceans form about 45% of the oxygen worldwide. Microscopic contrast method : Differential interference contrast. Magnification 400x at a print width of 10 cm.